考慮這個(非常醜陋的代碼)工作:NullPointerException異常而有狀態PartialFunction和collectFirst
object ExternalReferences2 {
import java.util.regex._
implicit def symbol2string(sym: Symbol) = sym.name
object Mapping {
def fromXml(mapping: scala.xml.NodeSeq) = {
new Mapping(mapping \ 'vendor text,
mapping \ 'match text,
mapping \ 'format text)
}
}
case class Mapping(vendor: String,
matches: String,
format: String) extends PartialFunction[String, String] {
private val pattern = Pattern.compile(matches)
private var _currentMatcher: Matcher = null
private def currentMatcher =
{ println("Getting matcher: " + _currentMatcher); _currentMatcher }
private def currentMatcher_=(matcher: Matcher) =
{ println("Setting matcher: " + matcher); _currentMatcher = matcher }
def isDefinedAt(entity: String) =
{ currentMatcher = pattern.matcher(entity); currentMatcher.matches }
def apply(entity: String) = apply
def apply = {
val range = 0 until currentMatcher.groupCount()
val groups = range
map (currentMatcher.group(_))
filterNot (_ == null)
map (_.replace('.', '/'))
format.format(groups: _*)
}
}
val config =
<external-links>
<mapping>
<vendor>OpenJDK</vendor>
<match>{ """^(javax?|sunw?|com.sun|org\.(ietf\.jgss|omg|w3c\.dom|xml\.sax))(\.[^.]+)+$""" }</match>
<format>{ "http://download.oracle.com/javase/7/docs/api/%s.html" }</format>
</mapping>
</external-links>
def getLinkNew(entity: String) =
(config \ 'mapping)
collectFirst({ case m => Mapping.fromXml(m)})
map(_.apply)
def getLinkOld(entity: String) =
(config \ 'mapping).view
map(m => Mapping.fromXml(m))
find(_.isDefinedAt(entity))
map(_.apply)
}
我試圖通過對如圖getLinkNew
使用collectFirst
改善getLinkOld
的方法,但我總是得到NullPointerException
因爲_currentMatcher
是仍設置爲null
scala> ExternalReferences2.getLinkNew("java.util.Date")
Getting matcher: null
java.lang.NullPointerException
at ExternalReferences2$Mapping.apply(<console>:32)
at ExternalReferences2$$anonfun$getLinkNew$2.apply(<console>:58)
at ExternalReferences2$$anonfun$getLinkNew$2.apply(<console>:58)
at scala.Option.map(Option.scala:131)
at ExternalReferences2$.getLinkNew(<console>:58)
at .<init>(<console>:13)
at .<clinit>(<console>)
at .<init>(<console>:11)
at .<clinit>(<console>)
,同時它與getLinkOld
完美。
這裏有什麼問題?
謝謝!你認爲什麼樣的解決方案不會計算兩次? – soc
提出了一種解決方法,可以對代碼進行最小限度的更改,而不是作爲有更多空間的評論。 –